Offices A GUIDE TO ENERGY EFFICIENT AND COST EFFECTIVE LIGHTING 50%

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1 Offices A GUIDE TO ENERGY EFFICIENT AND COST EFFECTIVE LIGHTING This guide provides information on how to improve the quality, visual comfort and costeffectiveness of lighting schemes in offices by using energy efficient lighting technologies and techniques. By following this guidance you can reduce your electrical energy consumption by 30% to 50%, reduce maintenance costs and improve the visual working conditions for staff. up to 50% savings OFF, 11, 03

2 ENERGY EFFICIENT AND COST EFFECTIVE LIGHTING Office lighting systems are a dominant user of electrical energy and a source of internal heat that often needs to be removed from the space. Modern energy-efficient lamps, luminaires (fittings) and controls can often reduce energy consumption by up to 50%. Specifying a well-controlled, high-quality, energy-efficient lighting system that can take advantage of available natural light can provide an effective and comfortable working environment for occupants. LIGHTING REQUIREMENTS AND TECHNIQUES Offices can be cellular or open-plan and the tasks carried out can have very different lighting requirements. However, following some essential guidelines can deliver effective lighting solutions that also minimise energy consumption. Use the most efficient lamps and luminaires (fittings) to light the entire volume of a space Ensure that the lighting is appropriate for tasks and office layouts Use appropriate lighting controls for both presence and daylight Minimise lighting requirements by availing of daylight and using light-coloured walls and ceilings Maintain and clean lamps and luminaires regularly Lighting the entire volume of a space, or volumetric lighting, results in a better visual environment, making a space feel brighter and larger. By lighting a number of different surfaces in the space rather than concentrating on the desktop alone, a softer and more natural lighting effect is achieved (as shown in Figure 1). The traditional approach to general office lighting is to install luminaires that are designed for use with computer screens. On their own these luminaires can create a gloomy visual appearance, with shadowing beneath furniture and other equipment (Figure 2). A more pleasant visual environment can be achieved by following the rules of thumb shown in Figure 3. 10% of desk lighting level on ceiling 50% of desk lighting level on walls 300/500 lux on desk Fig. 1 Lighting the volume of the space Fig. 2 Room has a gloomy appearance with heavy shadowing Fig. 3 Rules of thumb for getting a better lighting balance COLOUR TEMPERATURE AND COLOUR RENDERING The colour qualities of a fluorescent tube are characterised by two aspects: colour temperature colour rendering Colour temperature defines a lamp s whiteness, which is either blueish (cool) or reddish (warm) in appearance. This is measured in kelvin (K) (as shown in Figure 4). A colour temperature of less than 3,500 K is warm ; a colour temperature of 3,500 K is mid-white; and a colour temperature of 3,500 K and above is cooler. The colour temperature of different office lamps is given in the table at the back of this guide. Colour rendering is the ability of a light source to give good colour representation of the colour it is illuminating. It is measured on a scale of Ra 0 100, where Ra 100 represents the best, which is equivalent to that provided by daylight. In offices where accurate colour judgment is required (Ra 80 90), a triphosphor-type tube is necessary. Where colour rendering is of moderate importance (Ra 60 80), a halophosphor-type tube is sufficient, although these will be shortly phased out. Fluorescent tubes are classified by a specific code that indicates their characteristics, as shown in Figure 5. The last three digits of the reference number on many fluorescent lamps represent a method of specifying a lamp s colour rendering and colour temperature. For example (Figure 5), for a 3-digit reference of 840, the first digit (8) refers to a colour rendering of 80 89, and the second two digits (40) refer to the colour temperature, where 40 = 4,000 K. Fig. 4 Colour temperature (K) of various light sources Fig. 5 Fluorescent tube lamp codes 1

3 APPLICATIONS IN OFFICE AREAS The most efficient lamps to use in all office areas are tubular fluorescents and compact fluorescents. For localised accent effects, metal halides or low-voltage dichroics can be used. For task lighting at workstations, desk-lights with LEDs are now an option, or else use the traditional compact fluorescents. The lighting levels in occupied spaces should range from lux. In circulation routes, utility rooms, and stairwells, lux is adequate. Refer to page 5 for recommended lamp technical information. All fluorescent luminaires (light fittings) should incorporate electronic high frequency (EHF) control gear to maximise energy efficiency when T8 fluorescent tubes are used. T5s are only available with EHF control gear. Electronic control gear and electronic transformers should be used for lamp types 3 and 4 respectively. general offices High ceilings: Illuminate upwards as well as downwards with wall mounted direct/indirect luminaires using compact fluorescents or metal halides (Fig. 6a). This is particularly relevant for office stairwells and atria with wall mounted or suspended direct/ indirect luminaires using compact fluorescent, tubular T5 or metal halide. Low ceilings: 2.2m or below, use T8 tubular fluorescents or compact fluorescents. Suspended lighting: This is the popular form of office lighting and should be tubular T5 or compact fluorescent light sources. (Fig. 6b). T5 fittings are best suited to higher mounting positions. Fig. 6a Upward and downward lighting from wall sconces Task lighting: Use individual desk lamps with LEDs or compact fluorescents Fig. 6b Suspended lighting with sloping roof meeting rooms You should design for the appropriate light level on the table surface ( lux) but also provide ambient light by lighting vertical surfaces. This can be done with wall sconces (Figure 7) or asymmetric luminaires mounted close to walls. Ensure that lighting is controlled separately, i.e. wall lighting on one switch and the downward/upward lighting controlled by a separate switch. It is best if the lights closest to the wall used for presentations can be switched off, to provide good contrast for image projection Use tubular or compact fluorescents, and consider metal halide, low-voltage dichroics or LEDs for effect. Fig. 7 Meeting room reception Light vertical surfaces to create visual interest. To produce an impact effect the visual vertical surfaces need to be lit, this can be achieved utilising compact or tubular fluorescent lighting. Design for higher impact with localised accent lighting using metal halide lamps or low voltage dichroics or use more subdued lighting for a more ambient light level Fig. 8 Ambient Reception Area corridors and other circulation routes The illumination of the walls in corridors and stairwells provides a visually bright space and is best achieved with luminaires that have wide distribution patterns, e.g. using tubular or compact fluorescents. Ensure lights can be switched off automatically using daylight controls when lux is adequate. 1 2 Fig. 9 Lights off in corridor when daylight is sufficient 2

4 LUMINAIRES The luminaire is the complete lighting unit, consisting of the lamp and its housing/fitting. It is important for achieving the right lighting characteristics. Light Output Distribution Select luminaires with the right light output distribution. Light should be directed to the right part of the room using reflectors or diffusers which reduce obtrusive glare. Light Output Ratio (LOR) The LOR is the proportion of the lamp light output that emerges from the luminaire. The most popular type of louvered luminaire can have LOR values from 36% to 80%. Manufacturers provide graphical LOR information on their products as shown here these are similar products but they have large differences in light output. Choose the highest LOR to minimise the number of fittings that are required, reduce the energy consumption and to reduce maintenance and related costs to deliver the desired lighting effect. The luminaire in Fig 10a has a LOR of 0.53, i.e. only 53% of the lamp light output emerges from the luminaire, whereas that in Fig 10b has a LOR of 0.81, i.e. 81% of the lamp light output emerges from the luminaire. Fig. 10a The graph of the light emitted from a standard twin fluorescent luminaire with a reflector/louvre. The LOR total is 0.53 (53%) Fig. 10b The graph of the light emitted from a standard twin fluorescent luminaire with a reflector/louvre. The LOR total is 0.81(81%) controls Lighting controls are able to provide the right amount of light at the right place and at the right time. Some 40-60% of the installed load can be saved with good use of lighting controls. Lighting controls can: Dim the luminaires in response to daylight (with appropriate ballast) Provide the correct light level for different tasks and circulation areas. Provide presence detection to turn lights off if the area is unoccupied. Stop the artificial lighting from coming on when there is sufficient natural light. Be linked to time based controls to turn lights on or off depending on the time of day. Provide appropriate light levels and maximise energy savings. DAYLIGHT/deflecting BLINDS A well co-ordinated system of blinds and lighting controls can save 30-60% of electrical energy depending on winter/summer operation. Some office areas that receive good quantities of natural light could benefit from using daylight blinds. These blinds reduce glare and allow daylight to enter the space in a controlled way, instead of the standard horizontal or vertical blinds which cut out the light to the working space, especially when they are drawn, to alleviate glare or excess sunlight. There may be little need to use artificial lighting during normal office working hours, especially during sunny periods, if daylight blinds are installed. They are a great energy saving retrofit option. The figures below show how the blinds work in practice. The lower part of the daylightoptimised venetian blind with concaved mirror slats provides illumination deeper into the room. The upper slats, on the other hand reflect the sunlight against the ceiling and illuminate the room evenly. The daylight-optimised Venetian blind with concaved mirror slats provides for illumination of the depths of the room. If the sky is overcast or clear without the sun, the slat is folded up. In this way, the entire slat surface is available to guide the daylight into the workspace. The hinged slats reflect the direct sunlight. The rear part of the slat directs the incident daylight without glare. 3

5 MAINTENANCE AND LAMP REPLACEMENT There are great cost advantages to upgrading existing lamps and fittings. Recommendations for the most common lamp replacements are given below, complete with typical expected savings. Additional lamp comparisons are shown on page 5. When replacing lamps, ensure that the new lamp has comparable colour temperature and light output to the lamp it replaces. A proposed lamp type should be trialled in an area before any widespread lamp replacement. Lamp Type Replacement Lamp Type Benefits and Features Mains Voltage Tungsten Halogen 50W Mains Voltage Tungsten Halogen Dichroic Reflector 50W CFLi (GU10 Fitting) 7W 11W Low Voltage (12v) IRC Tungsten Halogen Dichroic 20W Over 80% energy saving Up to 7 times the lamp life of tungsten halogen Use for accent or feature lighting rather than general illumination As the light distribution differs between these two lamp types, lower light levels may be expected Requires warm-up period to come to full brightness Up to 40% energy saving 3 Times the lamp life of mains voltage tungsten halogen Mains Voltage Tungsten Halogen Dichroic Reflector 50W LED (GU10) (also available in low voltage) 4W 8W Up to 90% energy saving Up to 30 times the lamp life T12 (38mm) Fluorescent Tube (with conventional ballast) T8 (26mm) Halophosphor Fluorescent Tube T5 (16mm) High Output Fluorescent Tube with electronic adaptor conversion kit T8 (26mm) Triphosphor Fluorescent Tube 30% to 50% energy saving if the existing luminaires use switchstart or quick-start electromagnetic ballasts A conversion kit is required which includes the new electronic control gear (kits can also be used for t12 to t8 conversions) Further savings can be made by using fewer fluorescent tubes when the luminaires have opal or prismatic diffusers, which have no internal reflectors. The electronic adaptors are also available with clip-on reflectors, which can increase the luminaire light output by up to 50% and reduce the number of lamps required Up to 10% energy saving Twice the lamp life when used with electronic ballasts Use electronic control gear Note: Always use reputable suppliers and products that comply with all national and EU lighting regulations. Trial newer products for their suitability before widescale upgrades. Refer to for energy efficient products. 4

6 lighting technical details 1 Fluorescent tubes Fluorescent tubes are the most commonly used lamp types for offices. Types T8 (26mm) or T5 (16mm) with high colour rendering and of an appropriate colour appearance to provide the ambience required should be used as there are many different kelvin values available. 4 Low voltage dichroic lamps Low voltage (12v) dichroic lamps are available in many wattages and beam angles. The IRC (infra red coating) type is the most efficient with a 30W type providing equal if not more light than a standard 50W dichroic lamp. Always choose the correct beam angle according to the distance to the objects to be highlighted to ensure appropriate light levels. 2 Compact fluorescent lamps Compact fluorescent lamps are only available with high colour rendering and available in many different kelvin values. 5 LEDs LEDs are appropriate for signage, exit signs and desk lamps. 3 Metal halide discharge lamps Metal Halide CDM-T (HID) lamps have good efficiency and should be used to provide Highlight but can also be used for localised illumination. 6 Task lighting This may be under cabinet (fixed) or flexible arm desktop units. Fixed task lighting may use tubular or compact fluorescent and desk lamps can employ compact fluorescents or LEDs. Lamp Comparison Chart The best light sources for offices are highlighted in yellow, in the table below. Lamp Type Efficacy (Lumens per watt) Colour Temperature (K) Colour Rendering (Ra) Lamp Life (Hours) Daylight 5,500-8, Tungsten Mains Voltage 12 2, ,000-2,000 Tungsten Halogen Mains Voltage 18 3, ,000-8,000 IRC Tungsten Halogen Low Voltage (12v) 22 3, ,000 Compact Fluorescent ,700-4, ,000 T8 (26mm dia.) Halophosphor Fluorescent Tubes ,700-4, ,000 T8 (26mm dia.) Triphosphor Fluorescent Tubes ,700-6, ,000-60,000 T5 (16mm dia.) High Efficiency Fluorescent Tubes ,700-6, ,000 T5 (16mm dia.) High Output Fluorescent Tubes ,700-6, ,000 Metal Halide (Standard) ,000-6, ,000-10,000 Metal Halide (CDM) ,000-6, ,000 White Sodium , ,000 LED ,000-6, , ,000 Lamp life is the variance in lamp life indicated due to some lamp models having differing life-hours. One of the objectives of the office lighting design should be to ensure that the lamps and fittings chosen will require the minimum amount of maintenance. Always seek to use long-life versions to maximise savings in energy and maintenance costs. Colour temperature defines a lamp s whiteness. The higher the number, the cooler the colour. Colour rendering is the ability of a light source to give good colour representation of the colour it is illuminating. Efficacy is the ratio of light emitted by a lamp to the power consumed by it, i.e. lumens per watt. A lumen is a measure of the quantity of light emitted by a lamp. An Accelerated Capital Allowance is offered for lamp types that reach a minimum efficiency requirement. Further information, including a list of manufacturers and suppliers with eligible products, can be found on the SEAI website: 5